Takers in default - equity and trust

when the donee does not exercise power in general testamentary power of appointment or a special power of appointment, why the failure to exercise the power is treated analytically the same as the exercise of power for purpose of analyzing whether the interest in the takers in default violate the rule against perpetuities?

Is it true that the takers in default only becomes effective when the donee does not exercise the power at all? What does the last sentence actually mean?

and what is the role of second look doctrine here?

Also, in Sears v Collidege, why the court hold that the default takers under both provisions would have violated the Rule against Perpetuities if tested 'as of the moment the trust was created, the settlor retained the power to amend the trust until his death"?

And therefore, the court treated as such even if the power is not exercised for the purpose of the Rule against Perpetuities??